I'm writing a Node/Express app (my first) and need help persisting what feels like a global variable across page loads; but using a global variable feels wrong.
For the purposes of the question, the site is essentially 3 different table views on the same data. The data in the tables is taken from 3 separate MongoDB tables, merged together with a function, and displayed (using Pug, iterating over the object I just created).
The 3 different views are just different Pug templates iterating over the same object.
I have middleware which generates this object from MongoDB and stores it on res.locals, but I don't want to re-generate it by default every time the user selects a different view. The data hasn't changed, and this feels wasteful.
I want to be able to set some sort of variable, dataNeedsToBeUpdated, and if true then the function inside my middleware will actually do the work and regenerate the table; if false, it'll just skip the operation.
If the user performs one of my update operations, I'll set dataNeedsToBeUpdated = true, redirect, middleware will fire, and the data will refresh before the next page load.
How do I do this properly?
app.locals works just about like res.locals, just it's available to the whole app. You can access it in middleware from req.app.locals. The flow as you've described it sounds good; just use app.locals for storing the data and the dataNeedsToBeUpdated.